1. Field of the Invention
The present invention relates to scroll-type fluid displacement apparatus. More particularly, the present invention relates to a sealing mechanism of a scroll-type refrigerant compressor used in an automotive air conditioning system.
2. Description of the Related Art
A sealing mechanism of a discharge chamber defined between a housing and a scroll member used in a scroll-type fluid displacement apparatus is known in the art and is described in U.S. Pat. No. 5,336,058. Thus, the scroll-type fluid displacement apparatus includes a housing having an inlet port and outlet port and a fluid displacement mechanism within the housing for displacing a fluid from the inlet port to the outlet port. The fluid displacement mechanism is fixed to the housing by a plurality of fixing bolts. A discharge chamber is defined by the displacement mechanism and the housing, such that an O-ring seals the matching surface between displacement mechanism and the housing.
Further, FIGS. 1 and 2 depict a sealing mechanism of a discharge chamber defined between a housing and a scroll member used in a scroll-type refrigerant compressor without using an O-ring seal, as in an earlier technology. A housing 1 is formed of a cup-shaped casing 2 and a funnel-shaped front end plate 3 which closes the open end of casing 2. Casing 2 is provided with a fluid inlet port (not shown) for introducing fluid into housing 1, and a fluid outlet port 210 for discharging the fluid from housing 1. A fixed scroll member 10 has a first plate 11 of a substantially circular shape and a first spiral element 12 formed on a first face of first plate 11. Fixed scroll member 10 also has female threaded openings 16 which engage bolts 5 inserted through apertures 6 from outside of housing 1. Thereby, fixed scroll member 10 is formed between first plate 11 and the inner surface of casing 2. A discharge chamber 17 is in communication with a discharge port 13 and fluid outlet port 210.
An orbiting scroll member 20 has a second plate 21 of a substantially circular shape and a second spiral element 22 formed on a first face of second plate 21. Orbiting scroll member 20 is assembled with fixed scroll member 10, so that second spiral element 22 engages first spiral element 12 with a phase deviation of 180 degrees. This engagement forms a plurality of sealed off fluid pockets 23 between fixed scroll member 10 and orbiting scroll member 20. Second plate 21 is provided at its second face with a boss 24. A bushing 26 is disposed inside boss 24 with a needle bearing 25 therebetween. Bushing 26 has an eccentric aperture 26a and a pin 26b. Bushing 26 also is provided with counter weight 27 for canceling centrifugal force created by orbiting scroll member 20. A rotation preventing thrust bearing mechanism 28 is disposed between second plate 21 and front end plate 3 and prevents the rotation of orbiting scroll member 20 on its axis during revolution of front end plate 3 along a substantially circular path. Fixed scroll member 10 and orbiting scroll member 20 are assembled together to form a space, i.e., a suction chamber 29, between the inner peripheral surface of casing 2 and the outer peripheral surface of fixed scroll member 10 and orbiting scroll member 20. Suction chamber 29 is in communication with the fluid inlet port (not shown). Further, a plurality of reed valve members 40 cooperate with discharge port 13 at rear end surface of first plate 11. Reed valve members 40 control the opening and closing of discharge port 13 in response to a pressure differential between first discharge chamber 17 and a central pocket of fluid pocket 23. A retainer 41 is provided to prevent excessive bending reed valve member 40 when discharge port 13 is opened. An end of each of reed valve members 40 is fixedly secured to first plate 11 of fixed scroll 10 by a single bolt 43, together with one end of retainer 41.
A drive shaft 31 has a small diameter portion 31a and a large diameter portion 32 provided at opposite portions. Small diameter portion 31a is rotatably supported by a ball bearing 33 disposed inside one end of front end plate 3. Large diameter portion 32 is rotatable supported by a ball bearing 34 also disposed inside one end of front end plate 3, and large diameter portion 32 is provided at an eccentric position with a crank pin 35, which is inserted into eccentric aperture 26a in bushing 26.
Thereby, drive shaft 31 and orbiting scroll member 20 are connected, so that the orbiting scroll moves orbitally in accordance with the rotation of drive shaft 31. Large diameter portion 32 also is provided with arc-shaped grooves 36 for receiving pin 26b of bushing 26. The arc of grooves 36 has a center coincident with the center line of crank pin 35. Due to the engagement of one of grooves 36 by pin 26b, the rotation of bushing 26 around crank pin 35 is restricted. Counter-weight 27 for canceling centrifugal force created by orbiting scroll member 20 is thereby attached to drive shaft 31. The end of drive shaft 31 is connected to an electromagnetic clutch 38 mounted on the outer end of plate 3.
Casing 2 includes an annular sealing surface 2a formed inside of casing 2 and an annular rib 14 formed at the rear end of casing 2. Annular rib 14 is provided with a plurality of projecting portions 14a projecting toward the longitudinal axis of the compressor. Each projecting portion 14a of annular rib 14 has respectively aperture 6 formed therein, which is penetrated by bolt 5. Annular rib 14 has a sealing surface 14b facing toward a rear end surface 11 a of first plate 11 of fixed scroll member 10 and is inclined to sealing surface 2a of casing 2 at a 90 degree angle. Consequently, the matching surfaces between annular sealing surface 2a of casing 2 and side surface 11b of first plate 11 of fixed scroll 10 are sealed in surface contact by forcible insertion. Further, the matching surfaces between rear end surface 11a of first plate 11 of fixed scroll member 10 and sealing surface 14b of annular rib 14 are sealed in surface contact.
In this arrangement, the matching surfaces between rear end surface 11a of first plate 11 of fixed scroll member 10 and sealing surface 14b of annular rib 14 are sealed in surface contact. In particular, the matching surfaces are tightly sealed at around bolts 5, i.e., a first area ".alpha.," shown by hatching, because bolts 5 firmly engage fixed scroll member 10 through aperture 6 of annular rib 14 of casing 2. Referring to FIG. 2, an axial gap created between rear end surface 1 a of first plate 11 of fixed scroll member 10 and sealing surface 14b of annular rib 14 increases at points distant from bolts 5 because the tight force, which bolts 5 exert to tighten rear end surface 11a of first plate 11 of fixed scroll member 10 to sealing surface 14b of annular rib 14, decreases at points distant from bolts 5. Thereby, a small gap is created at a second area ".beta.," which is between adjacent bolts 5 on rear end surface 11a of first plate 11 of fixed scroll member 10 and sealing surface 14b of annular rib 14. As a result, discharge gas in discharge chamber 17 tends to leak from this gap.